Distortion and noise problems of subcarrier multiplexed optical systems, Journal of Telecommunications and Information Technology, 2001, nr 4

In this paper investigation of subcarrier multiplexed optical subsystems for optically supported communication systems is presented. Noise and spurious free dynamic range are the main parameters, which are determined by the applied optical transmission. The frequency dependence of these parameters and optimal frequency chosen is presented

Optimisation of Optical Network for Continuous-Variable Quantum Key Distribution by Means of Simulation

The unprecedented breakthrough in the field of quantum computing in the last several years is threatening with the exploitation of our current communication systems. To address this issue, researchers are getting more involved in finding methods to protect these systems. Amongst other tools, quantum key distribution could be a potentially applicable way to achieve the desired level of protection. In this paper we are evaluating the physical layer of an optical system realising continuous variable quantum key distribution (CVQKD) with simulations to determine its weak points and suggest methods to improve them. We found that polarisation dependent devices are crucial for proper operation, therefore we determined their most defining parameters from the point of operation and suggested extra optical devices to largely improve transmission quality. We also paid attention to polarisation controlling in these sort of systems. Our findings could be valuable as practical considerations to construct reliable CVQKD optical transmission links

Vertical cavity surface emitting lasers in radio over fiber applications, Journal of Telecommunications and Information Technology, 2003, nr 1

Theoretical and experimental study of using direct modulated vertical cavity surface emitting lasers in radio over fiber applications is presented. The nonlinear distortion and signal to noise ratio are investigated and evaluated in case of short-range multi-carrier transmission. Nonlinear characterization and comparison of the different kind of semiconductor lasers are also presented

Amplified spontaneous emission based quantum random number generator

There is an increasing need for true random bits, for which true random number generators (TRNG) are absolutely necessary, because the output of pseudo random number generators is deterministically calculated from the previous states. We introduce our quantum number generator (QRNG) based on amplified spontaneous emission (ASE), a truly random quantum physical process. The experimental setup utilizes the randomness of the process. In this system, optical amplifiers (based on ASE) play the major role. The suitable sampling rate is selected in order to build the fastest generator, while avoiding the correlation between consecutive bits. Furthermore, the applied post-processing increases the quality of the random bits. As a results of this, our system generated random bits which successfully passed the NIST tests. Our real-time generation system – which is currently a trial version implemented with cheap equipment – will be available for public use, generating real time random bits using a web page

Új fotonikai eszközök távközlési funkcióinak vizsgálata = Investigation on new photonic devices for telecommunication functions

A kutatások célja annak felderítése volt, hogy az új fotonikai eszközökkel milyen új távközlési feladatok oldhatók meg. Vizsgálatainkat a következő eszközökre terjesztettük ki: - VCSEL (vertical cavity surface emitting laser = függőleges üregű felületi sugárzó lézer) - SOA (semiconductor optical amplifier = félvezető optikai erősítő) - MCL (mikro-chip szilárd test lézer) - HPT (heterojunction photo transistor = hetero szerkezetű foto-tranzisztor) A következő főbb jellemzőket vizsgáltuk: - a jelelőállítás terén: módustisztaság, relatív intenzitás zaj (RIN), relaxációs rezonancia, modulációs meredekség és linearitás, hatásfok, stabilitás, stb. - az erősítés terén: spontán emissziós zaj, sávszélesség, erősítés, stabilitás, modulációs tulajdonságok, nemlinearitás, intermodulációs torzítás, keverés, stb. - a detekció terén: kvantum hatásfok, detekciós erősítés, zajtényező, sávszélesség, illesztés. A fenti vizsgálatok alapján új optikai távközlési eljárást dolgoztunk ki és vizsgáltunk meg. Az új rendszer épületek belső távközlésének a megoldására előnyösen használható. | The aim of the research was to disclose new application areas in telecommunications utilizing new photonic devices. The investigations were carried out on the following devices: - VCSEL (vertical cavity surface emitting laser) - SOA (semiconductor optical amplifier) - MCL (micro chip solid state laser) - HPT (heterojunction photo transistor) The following important characteristics were tested: - for signal generation: single mode operation, relative intensity noise (RIN), relaxation resonance, modulation sensitivity and linearity, efficiency, stability, etc. - for amplification: spontaneous emission noise, bandwidth, amplification, stability, modulation properties, nonlinearity, intermodulation distortion, mixing, etc. - for detection: responsivity, detection gain, noise factor, bandwidth, matching. Based on the beforegoing investigations, we developed and tested a new optical telecommunication method. The new system can be advantageously used for the internal communications in large buildings